We wish to examine why and how immunoglobulin proteins are produced and excreted in mouse myeloma cells only during a specific phase of the cell cycle. We will use synchronized mouse myeloma cells to examine: (1) By sucrose gradient centrifugation, the formation and degradation pattern of immunoglobulin producing polysomes throughout the cell cycle. (2) By in vivo labeling with (H3) uridine and the use of metabolic inhibitors, the attachment of the labeled mRNA to ribosomes by sucrose gradient centrifugation. From this data we will determine in what part of the cell cycle immunoglobulin mRNA is made. (3) By isolating immunoglobulin producing polysomes, extracting the RNA, treating with RNase and analyzing the RNase resistant poly (A) sequences by polyacrylamide electrophoresis, whether there is a change in the poly (A) sequences attached to the immunoglobulin in RNA molecule with time during immunoglobulin protein production. (4) In a cell-free system derived from G1 synchronized myeloma cells and with isolated active immunoglobulin mRNA, the presence of immunoglobulin specific factors.